How to limit collision..

Try changing the mass in the physics component and/or scale in the transform component of your objects.

Collision force is relative to speed and mass. A workaround to such behaviour is to increase the mass when the speed reaches some high values.

But keep in mind that the difference of two masses should not be greater than an order of 10 in the general case (order of 100 at the most). Otherwise your object can be send into orbit, or worse and unpredictable behaviours can happen.

Note that the documentation speaks of mass value between 0.1 and 10. But in my experience it is better to use higher values for high speed race game.

Also the bouciness can help absorb part of the energy produced upon collision.

The physic material has the greatest effect on the collision response, so play around with the settings. Create a physics material and assign it to your collider.